The present invention relates to a new and improved method of fabricating gears with rolled or generated tooth flanks by cutting-out tooth slots or spaces by means of at least one face-mill cutter head which performs a rotational movement about a cutter head axis, and furthermore, relates to a new and improved gear cutting machine for the performance of the aforesaid method.
There is already known to the art a method of fabricating gears according to the foregoing. With this prior art method the face-mill cutter head, in order to cut-out tooth slots or spaces, carries out in relation to the workpieces, apart from the rotational movement along a cutter head axis, only a generating or rolling motion, but no plunge-cut motion. The feed, and therefore the depth of penetration of the cutters into the workpiece thus occurs in the direction of the rolling or generating movement. As a result, rolled or generated toothed slots are formed during one machining operation.
With this method the individual cutting edges of the cutters or cutter blades of the face-mill cutter head are non-uniformly loaded. The cutting edge which first reaches the workpiece during the generating or rolling motion must perform the greatest cutting work, and therefore, also must again be first reground. Experience has shown that the highly loaded cutting edge must in fact be reground a number of times, whereas the remaining cutting edges need only be reground once. The grinding of the cutter or cutter blade is associated with an interruption in production, the duration of which is not only dependent upon the number of cutting edges which must be reground, but also upon the therewith associated work, such as dismantling of the cutters, adjusting the cutters and so forth.
Furthermore, there is known from U.S. Pat. No. 3,583,278 a method of manufacturing bevel gears, wherein the tooth slots or spaces constrict in the lengthwise direction of the teeth. With this method during a first step the tooth slots are roughed only by plunge cutting. The plunge-cut begins at the region of an end surface of the bevel gear or at an end region of the tooth slot which is to be fabricated, and with increasing tooth slot depth there also increases the length of the tooth slot. After the tooth slot or space has reached a depth which is still appreciably less than the desired final depth of the finish rough cut tooth slot, then there is initiated a rolling or generating operation. Now the tooth slot also is further cut in the lengthwise direction, so that it extends up to the other end surface of the bevel gear. Hence, there has been cut-out a tooth slot or space, the depth of which must be increased and the flank profile of which must be further improved upon.
This is accomplished during a further working step, in that the tooth slot is further machined at the tooth root or base as well as at the tooth flanks, so that after the second working step the tooth slots have a shape which comes closer to that of the finished machined tooth slots.
During the fabrication of rough cut tooth slots according to the above-described method there are used different cutter heads. To cut the tooth slots to a first limited depth there are provided wide cutters, by means of which it is not possible to cut to the complete tooth slot depth. During the subsequent further rough cutting to a greater tooth slot depth it is then necessary to employ narrower, less efficient cutters.
However, this method only has an apparent similarity with the method of the present invention, since it is concerned with only part of the method for rough cutting the tooth slots. Further operating steps of the prior art method under consideration for the finish machining of such tooth slots are very cumbersome and entail a number of operating steps which must be carried out at different machines.